The new information, which appears to corroborate the theory that South African or Belgian mercenaries may have forced the plane carrying Mr. Hammarskjold and 15 others to crash in a conflict region of Africa, is far from conclusive.

But it has provided more fuel for questions about what powerful nations may still be withholding in their intelligence archives about the crash, a defining event nearly six decades ago in emerging post-colonial Africa.

Mr. Hammarskjold, a pipe-smoking Swedish diplomat whose name now adorns buildings in and around the United Nations headquarters in New York, was on a mission to settle a conflict over Katanga, a rebellious part of Congo, when his aircraft, a chartered DC-6, crashed just after midnight on Sept. 18, 1961.

The aircraft, named the Albertina, was just a few minutes from its destination: an airfield in Ndola, in what was then the British protectorate of Northern Rhodesia and is now Zambia.

Whether the crash was accidental has been at the crux of inquiries that have persisted to this day, generating many conspiracy theories that colonial-era mining interests, perhaps backed by Western intelligence agencies, had plotted to assassinate him.

The inquiries have turned Mr. Hammarskjold’s death into the biggest mystery in the history of the United Nations.

Now, as a prominent jurist retained by Mr. Hammarskjold’s most recent successor, António Guterres, is preparing what may be the final report on the crash, a documentary film has caused a stir by presenting what it has described as revelations.

The two-hour film, “Cold Case Hammarskjold,” by Mads Brugger, a Danish journalist, received mixed reviews when it debuted at the Sundance Film Festival last month. It suggested that a South African group of white mercenaries had not only played a role in the crash, but had also later plotted to infect South Africa’s black majority with AIDS through a fake vaccination campaign.

While the AIDS theory has been met with deep skepticism by a range of experts, its assertions about a South African mercenary connection to Mr. Hammarskjold’s death have not been dismissed so easily.

A few weeks before the premiere of “Cold Case Hammarskjold,” Alexander Jones, a former member of the mercenary group and an important figure in the film, was interviewed for 90 minutes in Sweden by a representative of the jurist who is preparing the United Nations report, according to Andreas Rocksen, a producer of the film.

Mr. Jones described a 1989 recruitment session for the group, the South African Institute for Maritime Research, in which photographs of the Hammarskjold crash site had been displayed and the group’s leader “referred to it as one of the most successful operations — taking down a dignitary,” Mr. Rocksen said.

Asked for comment, the jurist, Mohamed Chande Othman, the former chief justice of Tanzania, said he had received “information from a multiplicity of sources,” including “the makers of a recent film on this subject matter,” according to an emailed statement from his spokesman.

The judge also said he was still evaluating the information “in terms of whether it may be new information of relevance” and that he intended to submit his report to Mr. Guterres by June.

Neither the judge nor Mr. Guterres said they had seen the film. But a spokesman for Mr. Guterres, Farhan Haq, said that Mr. Hammarskjold’s death “remains one of the saddest, most tragic events in the history of our organization,” and that “a full accounting of what happened is way overdue.”

The film’s researchers also claim to have corroborated a theory that a now-deceased Belgian mercenary pilot, Jan van Risseghem, flying a French-built Fouga Magister belonging to the forces of Moïse Tshombe, the Katangese rebel leader, attacked and destroyed Mr. Hammarskjold’s plane.

The researchers interviewed a friend of Mr. Risseghem’s, Pierre Coppens, who said Mr. Risseghem had recounted the attack to him years later in Belgium.

That account, however, has been called into question by a German historian, Torben Gülstorff, who has traced documents showing that several Dornier twin-engine planes were sold to the Katangese rebel authorities.

Unlike the Fouga, the Dornier Do 28A had short takeoff and landing capabilities and could have used a short airstrip in the Congolese town of Kipushi to reach Ndola, while a Fouga, based much further away in the Congolese town of Kolwezi, would have been at the limits of its range.

In an article last year, Mr. Gülstorff wrote that “a Dornier Do 28A might be the plane that was used in a nighttime air-to-air attack” on Mr. Hammarskjold’s plane. But he said, “further research is necessary.”

Doubt also has been expressed about Mr. van Risseghem’s whereabouts on the night of the crash. In 1994, Bengt Rösiö, a Swedish diplomat and author who had interviewed Mr. van Risseghem, said in a paper titled “Ndola Once Again” that Mr. van Risseghem was “not in Katanga at the time of the Ndola crash since he was on leave in Belgium.”

But that assertion, too, seems undermined by documents published in a Belgian newspaper, De Morgen, last month, showing that Mr. van Risseghem apparently drew an advance on his salary as a mercenary for the Katangese authorities on Sept. 16, 1961.

New questions also have been raised about the precise cause of the Albertina’s destruction. An article last month in Counterpunch, a magazine based in Petrolia, Calif., suggested that the pilot had been trying for a controlled crash landing after an attacking plane hit it.

If the Albertina had not struck an enormous anthill, the article said, the “skinny trees would probably have arrested its forward movement in a fairly short distance and the passengers if they were strapped in would have a pretty good chance of walking away.”

Some of those colonial officials present in Ndola at the time, representing Britain, insist that there was no evidence of an aerial attack.

“I mapped out where every body was found in relation to the crash site and attended every post mortem,” said John Gange, a former detective senior inspector in the colonial police who examined the site hours after it had been located.

“Every single scrap of the aircraft was removed from the scene and examined by qualified engineers,” Mr. Gange said in an email. “Nothing untoward was found.”

“No bullets or bullet holes were found on any of the bodies or on any part of the wreckage,” he added.

In the absence of any definitive explanation, conflicting theories have proliferated, along with accusations that Western powers and the United Nations itself have obstructed successive inquiries.

Last November, Judge Othman directly accused Britain and South Africa of having failed to cooperate in his repeated requests for information.

This month, Hynrich W. Wieschhoff, whose father, Heinrich A. Wieschhoff, an adviser to Mr. Hammarskjold, died in the crash, said the United Nations had “done little to publicize the activities” of Judge Othman, had been “slow to fully declassify its own archives and still refuses to release some documents.”

In an article posted on PassBlue, a news website that focuses on the United Nations, Mr. Wieschhoff said the judge’s final report may offer more detail. Still, he said, “unless that report or a new sense of purpose by the U.N. can pry the facts out of Britain, the U.S. and other key states, what happened and why will once again fade unanswered into the past.”